How to fix "Queue is not empty after probing"

The second example is compiled-out by
github.com/LinuxCNC/linuxcnc/blame/maste...s274ngc_pre.cc#L1542
(But I am not clear why, the commit message doesn't really say: github.com/LinuxCNC/linuxcnc/commit/b96c...de5e67d2dde0339bece3 )

So, it must be the first one causing the issue.

Did you try adding a queue-buster as suggested? (Not that that is the right fix, but maybe it will tell us something)